Solar System Simulator
The planets on their real orbits, moving. Drag through a month, a year, a decade or a century, and zoom from the Earth and its moon all the way out to Neptune.
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Distances from the sun are in AU — one AU is the Earth's average distance, 149,597,870 km — and the angle is where the planet sits around its orbit, measured from the March equinox direction.
Why the view climbs a ladder instead of zooming smoothly
The solar system does not fit in one frame, and the reason is a ratio. What decides whether you can see anything is how many times bigger the outermost drawn orbit is than the innermost one:
So each rung is a view where something is legible, rather than a smooth zoom that spends most of its travel in frames where nothing is. The outermost rung keeps the inner four as a labelled knot on purpose — that is the shape of the solar system, and it is the part every evenly-spaced textbook diagram hides.
What is to scale here, and what is not
The orbits are to scale within each view. The planets are not, and cannot be: at the Saturn view Jupiter would be 0.045 of a pixel across and Earth 0.0041. The dots are sized to be seen, not measured.
The one exception is Earth & the Moon, and it is worth looking at for that reason alone: it is the only view on this site that is to scale in size and distance at the same time. The moon really does sit about 30 Earth-diameters away — far further than almost every diagram draws it, and close enough to fit on a screen.
How far anything actually gets
| Span | Mercury | Earth | Jupiter | Saturn | Neptune |
|---|---|---|---|---|---|
| Month | 123° | 30° | 2° | 1° | 0° |
| Year | 4.2 laps | 360° | 30° | 12° | 2° |
| Decade | 42 laps | 10.0 laps | 303° | 122° | 22° |
| Century | 415 laps | 100 laps | 8.4 laps | 3.4 laps | 218° |
Which is why the zoom and the span belong together. A month is the right span for Mercury and means nothing for Neptune; a century sends Mercury round 415 laps — an unreadable blur — while Neptune still has not finished a single lap, because one Neptune year is 165 of ours.
Make a link to a particular date
The date, the zoom and the span are all in the address bar, so copying the URL shares exactly what is on screen.
The other simulator
This one is about the whole system. If the question is where the sun and the moon are from where you are standing — what time the sun comes up, why tonight's moon is the shape it is — that is the Sun, Earth & Moon movement simulator, which has a page for every city and a slider over a day, a week or a month.
Also: sunrise & sunset by city · moon phase & moonrise · lunar eclipses · how the positions are worked out
Solar system simulator FAQ
Why does the view jump between zoom levels instead of scrolling smoothly? Because the solar system will not fit in one frame. Out to Mars the outermost orbit is only 4 times the innermost, and everything is separable. Out to Saturn it is 25 times and the inner four are a tight knot. Out to Neptune it is 78 times: Mercury's whole orbit is 3.0 pixels across and Earth's is 8. Each rung of the ladder is a view where something is legible; a smooth zoom would just pass through a lot of frames where nothing is.
Are the planets drawn to scale? The ORBITS are, within each view. The planets themselves cannot be: at the Saturn view, Jupiter — the largest planet — would be 0.045 of a pixel across, and Earth 0.0041. So the dots are legibility sizes, not measurements. The one exception is the Earth and Moon view, which is to scale in both size and distance at once — the moon really does sit about 30 Earth-diameters away, and that fits on a screen.
Where are the other planets' moons? Not drawn, deliberately. At the zoom where Jupiter is visible at all, its outermost large moon would be under half a pixel from it, and this simulator does not solve for their positions. Drawing them at invented distances in invented places would be two untruths in the service of a busier picture. Earth's moon gets its own view because at that zoom it is real.
How accurate are the positions? They come from Keplerian elements with per-century rates — the standard approximate-positions method — which is good to a few arcminutes over 1800–2050. That is far finer than this picture can show: at the outermost view, a whole degree of Neptune's orbit is under two pixels. It is not an ephemeris, though: no perturbations between planets, no relativity. For anything that needs to be right to the second, use a real ephemeris.
Why doesn't Neptune go anywhere? Because it takes 165 years to go round once. Press Play on a Century and Neptune covers 218° — not even one lap. Jupiter manages 8.4 laps in the same span and Mercury 415 laps, which is why the span control and the zoom level go together: a month means something for Mercury and nothing at all for Neptune.
Can I share a particular date? Yes. The date, time, zoom level and span are all in the address bar, so copying the URL shares exactly what is on screen, and the builder near the bottom writes one for you.